Upower warning level

[bartelsielski]

Add CSS class based on the 'warning_level' field reported by UPower over D-Bus. This makes it possible to add custom styling when the battery is near empty.

Example:

#upower {
	background-color: #24283b;
	color: #9ece6a;
}

#upower.low {
	background-color: #f7768e;
	color: #24283b;
}

@keyframes blink {
	to {
		background-color: #24283b;
	}
}

#upower.critical {
	background-color: #f7768e;
	color: #24283b;

	animation-name: blink;
	animation-duration: 0.5s;
	animation-timing-function: steps(12);
	animation-iteration-count: infinite;
	animation-direction: alternate;
}

Additionally, fixed some potential uninitialized reads.

[Alexays]

Nice, thanks!

[bartelsielski]

Seems I had some typos in the initialization values, my apologies. I've updated them (and checked that it compiles this time). And fixed the issues clang-format reported.